Various types of rechargeable batteries known in the art have been proposed as a power supply for a portable electronic device and a power supply for an electric vehicle, a hybrid vehicle, and the like. Among such rechargeable batteries, in particular, a sealed battery often includes a so-called return type safety valve that is actuated to open when the internal pressure of a battery case exceeds a predetermined pressure and lower the internal pressure, and returns to a closed state after the internal pressure is lowered. When chemical reactions of a power generation element generates gas or the like and causes an abnormal increase in the internal pressure, such a safety valve is actuated to discharge the gas from the case. The safety valve described in patent document 1 is known as such a return type safety valve used in the sealed battery.
As illustrated in FIG. 10, the safety valve described in patent document 1 includes a valve case 25 coupled to a battery container that accommodates a pole plate group of a positive electrode and a negative electrode, which form a battery. In the middle of a bottom wall of the valve case 25, a valve port 26 is arranged in communication with the battery container, and an annular seal projection 27 is formed around the valve port 26. The valve case 25 accommodates a valve body 31, which is formed from rubber or the like that is pressed against the seal projection 27. A valve lid 32 is engaged with an upper open end of the valve case 25 that accommodates the valve body 31. The valve lid 32 includes an open port 33 that is in communication with the internal space of the valve case 25. In the safety valve configured in such a manner, when the internal pressure of the battery is within the normally expected range, the seal between the seal projection 27 and the valve body 31 is maintained to isolate the inside of the battery from the outside so that the gas in the battery does not leak out. However, when the internal pressure of the battery abnormally increases and reaches a certain set value, the internal pressure opens (elastically contracts) the valve body 31, and gas is discharged out of the battery through between the seal projection 27 and the valve body 31.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-110388